The present invention relates to a presensitized plate useful for making a lithographic printing plate, which comprises a specific substrate provided thereon with a photopolymerizable light-sensitive layer containing a specific ethylenically unsaturated bond-containing compound. More specifically, the present invention pertains to a presensitized plate useful for making a lithographic printing plate, which comprises a combination of a substrate having a specific surface structure with a photopolymerizable light-sensitive layer containing a specific ethylenically unsaturated bond-containing compound having a specific structure and which does not show any reduction of the sensitivity and can provide a printing plate capable of simultaneously satisfying the requirements such as the resistance to staining and printing durability.
The lithographic printing technique is a printing system, which makes the most use of the fact that the oil, in itself, is not miscible with water and thus the lithographic printing plate used in this printing technique carries, on the plate surface, a region, which receives water, but repels the oil-based ink (hereunder referred to as “non-image area”) and a region, which repels water, but receives the oil-based ink (hereunder referred to as “image area”) formed thereon.
The aluminum substrate used for making a lithographic printing plate (hereunder simply referred to as “substrate for lithographic printing plate”) is used in such a manner that the surface thereof serves as non-image areas and therefore, it should have various reciprocal characteristic properties such as excellent hydrophilicity and water retention characteristics and excellent adhesion to the image-recording layer applied thereto.
If the hydrophilicity of the substrate is too low, ink is also adhered to the non-image area and this in turn results in the staining of the body of a blanket and in its turn the so-called scumming. Moreover, if the water retention of the substrate is too low, the clogging of shadowed portions is observed unless the amount of the dampening water is increased upon printing. For this reason, the so-called water tolerance becomes narrow.
To obtain a substrate for lithographic printing plate excellent in these characteristic properties, it is common to subject an aluminum plate to a surface-graining treatment (or a surface-roughening treatment) to thus impart unevenness to the surface. Regarding this unevenness, there have been proposed a variety of shapes as will be detailed below. Japanese Un-Examined Patent Publication (hereunder referred to as “J.P. KOKAI”) Hei 8-300844 discloses a triple structure comprising large, medium and small waves in which the pore sizes of the medium and small waves are specified. J.P. KOKAI Nos. Hei 11-99758 and Hei 11-208138 disclose a double structure comprising large and small waves in which the diameter of the small waves is specified. J.P. KOKAI Hei 11-167207 discloses a technique for imparting fine projections to the surface of an aluminum plate in addition to large/small double concaved portions (pits). Japanese Patent No. 2,023,476 discloses a double structure in which the pore size is specified. J.P. KOKAI Hei 8-300843 discloses a double structure whose factor: a30 indicating the surface smoothness is specified. J.P. KOKAI Hei 10-35133 discloses a structure, which is formed by a plurality of electrochemical surface-roughening treatments (hereunder also referred to as “electrolytic surface-roughening treatment(s)”) and in which the ratio of diameters of pits to be superposed.
In this surface-graining treatment, there have been used, for instance, mechanical surface-roughening methods such as ball graining, brush graining, wire graining and blast graining methods; electrolytic surface-roughening methods in which an aluminum plate was electrolytically etched in an electrolyte containing hydrochloric acid and/or nitric acid; and a composite surface-roughening method comprising a mechanical surface-roughening method and an electrolytic surface-roughening method.
In the foregoing conventional techniques, however, the resistance to staining and the printing durability are in the trade-off relationship and thus, the conventional techniques cannot simultaneously accomplish the foregoing two characteristic properties, or high resistance to staining and high printing durability.